The most basic ordinal concepts are more and less. To test when infants understand these concepts as they apply to numbers, Strauss and Curtis (1984) found that 16- to 18-month-olds have a rudimentary understanding of these concepts. Babies who had been reinforced for reaching for a square with 2 dots rather than 1, and then one with 3 dots rather than 2, subsequently selected a square with 4 dots rather than 3, thus indicating understanding of the ordinal property "more numerous". They also succeeded when the square with fewer dots was reinforced.